Load distribution in a speed reducer with two intermediate transmission lines

ABSTRACT

The invention relates to a speed reducer (10) with two intermediate transmission lines (16), in particular for a turbine engine, including an input line (12) and an output line (14) driven by the input line via said intermediate lines, said intermediate lines being substantially parallel, characterised in that it includes load-distribution means between said intermediate lines, said load-distribution means comprising ball-and-socket means (30) for rotatably coupling a first end of the input line, first means (34) for damping the radial movements of said end of the input line, and second means (34) for damping the radial movements of a second opposite end of the input line.

TECHNICAL FIELD

The present invention relates to a speed reducer with two intermediate transmission lines, in particular for a turbomachine.

PRIOR ART

The prior art notably comprises documents U.S. Pat. No. 3,772,934, EP-A1-0 636 813 and WO-A1-2013/150229.

A turbomachine can comprise one or more mechanical speed reducers. This is notably the case with a turboprop of which the propeller is pulled into rotation by a turbine shaft by means of a speed reducer.

There are many types of speed reducer such as planetary gear reduction mechanisms, chain gears, worm gears, intermediate transmission lines, etc. The present invention largely relates to a reducer with transmission lines (also known as a compound reducer).

In the current technology, a speed reducer of this type comprises an input line and an output line driven by the input line by means of two intermediate transmission lines. The power transmitted by the entry line is split between the intermediate lines before being transferred to the output line. The intermediate transmission lines are parallel and in general each comprise a shaft bearing an input gear meshing with the input line and an output gear meshing with the output line. By changing the number of teeth on the different gears, it is possible to obtain a reduction ratio between the input line and the output line. This structure allows a great reduction of speed in a confined space and with a controlled mass.

By definition, a reducer of this type is a statically indeterminate system. Without specific arrangement, it is possible for an intermediate line to have the majority of the motor power pass through it, while the other intermediate line sees practically no power flow.

Thus, there exists a need to distribute the load between the intermediate lines in a reducer of the above-mentioned type to ensure that half the power passes through each of the intermediate lines of the reducer.

One solution consists of providing a ball-and-socket means for swivel coupling one end of the input line, and means for damping the radial movements of an opposite end of the input line.

The input line is susceptible to move radially (with respect to its longitudinal axis). This is made possible by the fact that one of the ends of the input line is swivel mounted, with regard to, for example, a motor shaft. The opposite end of the input line can then move in a radial direction, these movements being damped. These means for swivelling and damping form the means for distributing the load, which functions in the following manner. If one of the intermediate lines is more loaded, that is to say the torque passing through this line is greater than that passing through the other line, then the stress, produced by the torque, on the input line gear is greater on one side than the other. A force will thus be applied to the input gear, which will lead to the radial movement of the input line. This movement will allow the plays to be rebalanced at the level of the input line. When balanced, the stress placed on the gear by the torque on the intermediate lines cancels out, which means the torque on the intermediate lines is equal.

However, this solution can lead to a gear misalignment. Due to this misaligned operation, a “crowning” type correction of the gear teeth is required. This correction leads to an increase in surface pressure on the teeth. In addition, if the misalignment is significant, it is not necessarily possible to ensure acceptable operation of the reducer, even with the application of crowning.

DISCLOSURE OF THE INVENTION

The present invention proposes a simple, efficient, and economical solution to the problem described above.

The invention proposes a speed reducer with two intermediate transmission lines, in particular for a turbomachine, comprising an input line and an output line driven by the input line by means of said intermediate lines, these intermediate lines being substantially parallel, characterised in that it comprises a means of distributing the load between said intermediate lines, this means of distribution comprising ball-and-socket means for swivel coupling a first end of the input line, first means for damping the radial movements of said first end of the input line, and secondary means for damping the radial movements of a second opposite end of the input line.

The principle behind the invention is to mount the input line on two distant means of damping. The invention allows the input line to move vertically without misalignment.

The reducer in accordance with the invention can include one or several of the following features, applied in isolation or in combination with one another:

-   said first and second damping means are configured to allow the     input line to move in a direction substantially perpendicular to a     plane passing substantially through the axes of the intermediate     lines, -   said first and second damping means comprise springs, preferably     return springs, -   said springs are identical, -   said first and second damping means comprise roller bearings, -   each of said first and second damping means comprises a roller     bearing which is mounted on said first or second end of the input     line, and which is supported by a spring, -   said first and second damping means are identical, -   said first and second damping means are mounted on both sides of an     input line gear, and -   said first and second damping means ( ) are situated equidistantly     from said gear; the rollers can be placed equidistantly from the     gear teeth to have the same movement on each roller and therefore to     avoid teeth misalignment.

The present invention also relates to a turbomachine, characterised in that it comprises at least a reducer as described above. The reducer can comprise an output line configured to drive a propeller not streamlined by the turbomachine.

Preferably, the turbomachine is an aircraft turboprop.

DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, features and advantages of the invention will become clearer upon reading the following description as a non-limiting example and with reference to the appended drawings of which:

FIG. 1 is a very schematic view of a speed reducer with two intermediate transmission lines, seen from the side,

FIG. 2 is a very schematic view of a speed reducer with two intermediate transmission lines, seen from the front,

FIGS. 3 and 4 are partial schematic views seen from the front of a reducer of the described type, FIG. 3 representing a non-homogeneous distribution of load between the intermediate lines and FIG. 4 a homogeneous distribution of load between the intermediate lines,

FIG. 5 is a very schematic view of an input line equipped with means of load distribution, and

FIG. 6 is a very schematic view of an input line equipped with means of load distribution in accordance with the invention.

DETAILED DESCRIPTION

FIG. 1 very schematically represents a speed reducer 10 with two intermediate transmission lines, said reducer 10 mostly comprising four parts: an input line 12, an output line 14 and two intermediate transmission lines 16 which are driven by the input line 12 and in turn drive the output line 14.

The different parts 12, 14, 16 of the reducer are in general mounted on a reducer casing which is not represented here, this reducer comprising a first opening for the passage of the input line and its connection to a first component of a turbomachine, for example, and a second opening for the passage of the output line and its connection to a second component of the turbomachine. For example, the first component is a turbine shaft of the turbomachine and the second component is a drive shaft of a propeller of that turbomachine in the case where the latter is a turboprop.

The input line 12 comprises a shaft 18 bearing a gear 20 with external teeth. The gear 20 and the shaft 18 are coaxial and turn around the same axis marked B.

The output line 14 comprises a shaft 22 bearing a gear 24 with external teeth. The gear 24 and the shaft 22 are coaxial and turn around the same axis marked A. Here they turn in the same rotational direction as the gear 20 and the shaft 18 of the input line.

The input and output lines 12, 14 are parallel. Their rotational axes A, B are thus parallel.

The intermediate transmission lines 16 are substantially parallel and identical. Each line 16 comprises a shaft 25 which bears an input gear 26 at a first end and an output gear 28 at a second end. The output gears 28 are meshed with the gear 24 of the output line 14. The input gears 26 are meshed with the gear 20 of the input line 12. The gears 26, 28 have external teeth. Each shaft 25 and its gears 26, 28 are coaxial and turn around the same axis marked C, parallel to axes A and B.

As previously explained, this type of reducer 10 is a statically indeterminate system and it is possible for an intermediate line 16 to have the majority of the motor power pass through it, while the other intermediate line sees practically no power flow. As seen in FIG. 2, this poor distribution of power or load is mainly due to the fact that, although the gears 26 are in contact with the gear 20 at points C, and the gear 28 of one of the intermediate lines is in contact with the gear 24 at point D, it is difficult to ensure a lack of play at E, between the gear 24 and the gear 28 of the other intermediate line.

The invention proposes a solution to this problem by equipping the reducer 10 with a means of distributing the load between the intermediate lines 16.

The general principle of the distribution of load is represented in FIGS. 3 to 5 and FIG. 6 represents an embodiment of the invention.

The shaft 18 of the input line 12 is susceptible to move radially (with respect to its longitudinal axis). This is made possible by the fact that one of its ends is swivel mounted (FIG. 5), with regard to, for example, the turbine shaft. The end of the shaft 18 comprises, for example, swivelling grooves 30 engaging with complementary grooves of a sleeve 32 connecting the input line of the reducer to the turbine shaft. Radial movements are to be understood here as the swivelling of the input line 12 around a point situated at the level of its swivelling end.

The opposite end of the shaft 18 of the input line 12 can thus move in a radial direction, these movements being damped by a spring 34.

If one of the intermediate lines 16 is more loaded (FIG. 3), that is to say the torque passing through this line is greater than that passing through the other line, then the stress f1, produced by this torque, on the input line gear 20 is greater on one side than the other. A force F will thus be applied to the input line gear 20, which will lead to the movement of the input line. This movement allows the plays to be rebalanced at the level of the input line. When balanced, the stress f1, f2 placed on the gear 20 by the torque on the intermediate lines cancels out, which means the torque on the intermediate lines is equal.

Advantageously, the damping means of spring 34 is combined with a roller bearing 36 guiding the shaft 18 of the input line 12.

As mentioned above, a gear misalignment can occur as illustrated in FIG. 5. Due to this misaligned operation, a “crowning” type longitudinal correction of the gear teeth is required. This correction leads to an increase in surface pressure on the teeth. In addition, if the misalignment is significant, it is not necessarily possible to ensure acceptable operation of the reducer, even with the application of crowning.

The invention allows this problem to be remedied thanks to the overall input line damping.

FIG. 6 represents an example of an embodiment of the invention, in which the elements described above are indicated by the same reference numerals.

Two roller bearings 36, of ball-type for example, are mounted on both sides of the gear 20, at the ends of the input line 12.

Classically, each bearing 36 can comprise two rings, internal and external respectively, between which a row of ball bearing extends which can be maintained by a ring cage. The internal ring of a first bearing 36 is mounted fixedly on an end of shaft 18 of the input line 12, opposite to its end comprising the swivelling grooves 30. The internal ring of the second bearing 36 is mounted fixedly on the end of the shaft 18 comprising the swivelling grooves 30.

The damping springs 34 support the bearings 36. A first spring 34 supports the first bearing 36, and a second spring 34 supports the second bearing 36. Preferably, the springs 34 are identical. Preferably the springs are return springs. Advantageously, they are situated equidistantly from the gear 20.

The end of the shaft 18 which comprises the swivelling grooves 30 is engaged with the complementary grooves of a sleeve 32 connecting the input line of the reducer to the turbine shaft.

The invention works as indicated previously in relation to FIGS. 3 and 4. As is visible in FIG. 6, if one of the intermediate lines 16 is more loaded (FIG. 3), that is to say the torque passing through the line is greater than that passing through the other line, then the stress f1, produced by this torque, on the input line gear 20 is greater than on the other side. A force F will thus be applied to the input line gear 20, which will lead to the movement of the input line, but it does not mean it will misalign thanks to the invention. 

1. Speed reducer with two intermediate transmission lines, in particular for a turbomachine, comprising an input line and an output line driven by the input line by means of said intermediate lines, these intermediate lines being substantially parallel, wherein it comprises a means of distribution of load between said intermediate lines, this means of load distribution comprising ball-and-socket means for swivel coupling a first end of the input line, first means for damping the radial movements of said first end of the input line, and secondary means for damping the radial movements of a second opposite end of the input line.
 2. Reducer according to claim 1, wherein said first and second damping means are configured to allow the input line to move in a direction substantially perpendicular to a plane passing substantially through the axes (C) of the intermediate lines.
 3. Reducer according to claim 1, wherein said first and second damping means comprise springs, preferably return springs.
 4. Reducer according to claim 3, wherein said springs are identical.
 5. Reducer according to claim 1, wherein said first and second damping means comprise roller bearings.
 6. Reducer according to claim 5, wherein said springs are identical, and wherein each of said first and second damping means comprises a roller bearing which is mounted on said first or second end of the input line, and which is supported by a spring.
 7. Reducer according to claim 1, wherein said first and second damping means are identical.
 8. Reducer according to claim 1, wherein said first and second damping means mounted on both sides of a gear of the input line.
 9. Reducer according to claim 8, wherein said first and second damping means are situated equidistantly from said gear.
 10. Turbomachine, wherein it comprises at least one reducer (10) in accordance with claim
 1. 